This is possible, and the Canadian part is a direct bolt-on. Some dealerships may get confused over what you are asking for, however. You may be able to get around this by ordering a Galant VR-4 alternator instead - it is also 90A and will bolt right on.
There are some indications in the archives that the 90 amp alternator is the same as the 75 amp U.S. stock alternator, except it is rated for 90A. (Read about this here.) Wes Grueninger asserts that the two alternators are, in fact, different, with the 90A having an extra output tap attached to the wye terminal in the diode rectifier pack. In any case, the 90A alternator has a rated minimum output of 50A, with a 90A typical output rating. Even Canadian DSMers complain that the alternator on the car is undersized.
Read this post by Gary Selph for a description of possible alternator replacement options, including the Mitsubishi part number for the Canadian alternator. Also read Dean's Daily Discussions #8 for a little encouragement on how simple the replacement process should be.
For auto owners, Kyle Zingg posted that the alternator for the auto cars has a different part number, at least for 1Gs. The part number for the 1G auto alternator is MD153843. Manual owners have the same alternator on both the turbo and 2.0L non-turbo engines. It has also been reported that 1G and 2G alternators are the same aside from the actual output plug, which can be swapped.
It has been reported that Mitsu alternators rotate in the opposite direction of most alternators, making aftermarket units problematic. Read about this here. For this reason it is possible that aftermarket parts may not ventilate correctly, leading to premature failure.
With the creation of at least two Canadian sub-regional chapters of Club DSM, those who find themselves in a bind may be able to work a deal with a Canadian DSMer to provide a Canadian alternator. Owing to logistical difficulties, currency exchange and the possibility of taxes and/or duty on the imported part, this should be considered as a last-resort option.
As a companion to this question, you will likely want to read the Battery FAQ, and the dead battery question in this file.