It looks like it's going to be a hassle bringing the car south from Canada - and it's not only cat changes that may be required. Read what I've copied (below) from the website http://www.buyclassiccars.com/import.asp.
I hope this helps you.
Regards,

VEHICLE IMPORTATION GUIDELINES
(Imported From Canada)

All passenger cars less than 25 years old imported for personal use (not resale) into the U.S. on a permanent basis from Canada should follow this procedure. This process may also be followed if a vehicle was originally imported from Canada on a temporary basis or if prior DOT or U.S. Customs clearance was not obtained.

Contact the manufacturer of the vehicle, and ask if the vehicle complies with all applicable U.S. Federal motor vehicle safety standards (FMVSS). The letter from the manufacturer must identify your vehicle by the Vehicle Identification Number (VIN). READ THE LETTER CAREFULLY.

If the manufacturer letter states that the vehicle complies with U.S. FMVSS, except for minor labeling requirements, you have an acceptable letter. This letter along with your vehicle registration should be presented to U.S. Customs at the border. U.S. Customs will review the manufacturer letter to assure that the vehicle complies.

If the manufacturer letter states that the vehicle meets all U.S. FMVSS, except for the speedometer, or headlights, you may have these components replaced at a dealer authorized by the factory to repair your vehicle. In addition to the documents cited above, you must present the invoice for the speedometer or headlight replacement to obtain U.S. Customs approval.

If the manufacturer letter states that the vehicle meets all U.S. FMVSS except for FMVSS No. 208 (automatic or passive restraint requirements) you WILL NOT be able to bring your vehicle into the U.S. on a permanent basis unless it is modified by an RI. If an RI is willing to modify the vehicle, it may be expensive and may change your desire to import the vehicle.

If the manufacturer will not issue a letter for your vehicle, the only method to import your vehicle on a permanent basis is to contract with an RI.

EPA approval is also required. You may call the EPA information line at: (202) 564-9660.

VEHICLE IMPORTATION GUIDELINES
(Imported from a country other than Canada)

The following provides information concerning the importation of a passenger car built to comply with the standards of a country other than the U.S. or Canada. Importers of motor vehicles must file form HS-7 (available at ports of entry) at the time a vehicle is imported to declare whether the vehicle complies with DOT requirements. As a general rule, a motor vehicle less than 25 years old must comply with all applicable Federal motor vehicle safety standards (FMVSS) to be imported permanently. Vehicles manufactured to meet the FMVSS will have a certification label affixed by the original manufacturer in the area of the driver-side door. To make importation easier, when purchasing a vehicle certified to the U.S. standards abroad, a buyer should have the sales contract verify that the label is attached and present this document at time of importation.

A vehicle without this certification label must be imported as a non-conforming vehicle. In this case, the importer must contract with a DOT-Registered Importer (RI) and post a DOT bond for one and a half times the vehicle's dutiable value. This bond is in addition to the normal Customs entry bond. Copies of the DOT bond and the contract with an RI must be attached to the HS-7 form.

Under the contract, the RI will modify and certify that the vehicle conforms with all applicable FMVSS. Before an RI can modify a vehicle NHTSA must have determined that the vehicle is capable of being modified to comply with the FMVSS. If no determination has been made, the RI must petition NHTSA to determine whether the vehicle is capable of being modified to comply with the FMVSS. If the petitioned vehicle is not similar to one sold in the U.S., this process becomes very complex and costly. A list of vehicles previously determined eligible for importation may be obtained from an RI or from the NHTSA web site.

Since the cost of modifying a non-conforming vehicle, or the time required to bring it into conformance, may affect the decision to purchase a vehicle abroad, it is recommended that you discuss these aspects with an RI before buying and shipping a vehicle to the U.S.

For federal regulations concerning vehicle emissions contact the Environmental Protection Agency, Manufacturers Operations Division, EN-340, 401 M Street SW, Washington, DC 20460, Tel: (202) 564-9660. Information concerning duty or other Customs matters can be obtained from the Classification and Value Division, U.S. Customs Service, Washington, DC 20229, Tel: (202) 927-0300, or http://www.customs.ustreas.gov/travel/auto.htm

For information regarding registration or operation of a properly imported vehicle in a specific state, we advise you to contact the Department of Motor Vehicles or other appropriate agency in that state since the requirements vary by state.

Registered Importers

Autosport Design
203 West Hills Road,
Huntington Station, New York, 11746 USA
Tel: 516 248 0066
Fax: 516 248 4422

G & K Automotive Conversion
3231 South Standard Avenue
Santa Ana, CA 92705 USA
Tel: 714 545 9503
Fax: 714 545 7667

Sunshine Car Import
745 NE 19th Place
Cape Coral, FL 33903
Tel: 941 458 1020
Fax: 941 458 4410

Wallace Environmental Test Lab
2140 Wirtcrest
Houston, TX 77055 USA
Tel: 713 956 7705
Fax: 713 956 0104

Automotive Importers
1730 SouthFirst Street
Yakima, WA 98909
Tel: 509 248 4700
Fax: 707 839 1662


Northern California Diagnostic Lab
2748 Jefferson St.
Napa, CA 94558
Tel: 707 258 1611
Fax: 707 258

European Auto Repair Center
6845 SW 59th Place
Miami, FL
Tel: 305 661 2939
Fax: 305 662 2105

JK Technologies
3500 Sweet Air Street
Baltimore, MD 21211 USA
Tel: 410 366 6332
Fax: 410 366 7655 Western Cascade
12065 44th Place S.

Tukwila, WA 98178 USA
Tel: 206 243 2667
Fax: 206 767 2157
Black Shrine
1760 Monrovia Avenue, Unit C-12
Costa Mesa, CA 92627 USA
Tel: 949 515 8056
Fax: 949 515 8036

Potsdam Importers
7513 USH 11
Piotsdam, NY
Tel: 315 265 1850