Wellll...Canadian law does prohibit portable toilets. But a lot of Americans with small boats visit the Canadian waters and I've yet to hear of any US flagged boat who's been cited or been turned back at the border or customs check-in for having one. I'm not sure I've ever even heard of any US vessel that's even been inspected. However, if you're gonna be there long enough to need to empty the portapotty tank, THAT could cause you problems.
So the best solution MIGHT be to replace the portable with an MSD version ("MSD" in the model number means it has the fittings to install a vent line and pumpout line). The 5-6 gal models hold 50-60 flushes...being able to pump out instead of having to carry even the small one ashore to dump it would certainly make your life easier...and the larger capacity--which fits the same footprint as the 2-3 gal portables, btw--would let you stay out longer wherever you go.
The sbo online store carries the two best ones--the Thetford 550P MSD
Theford Porta pottie 550P and the Dometic/SeaLand Sanipotttie 965MSD
SaniPottie MSD They also have the deck pumpout fitting...check availability of 1.5" pumpout hose and 5/8" vent line.