Yeah, can second the 100% audit rate by CRA. I've claimed foreign tax credits over the last several years due to RSUs vesting from my time in the US (intra-company transfer). The audits are not pleasant and the letters sound threatening. However, by now my accountant and I have templatized the CRA responses. Typically they want a copy of your US tax transcript. It's easy to order one from the IRS. Overall. it's like doing a second tax return at the end of the year, and they've accepted my responses each time.Undoubtedly, hiring an accountant would be not only prudent, but I would deem a necessity if one were to incorporate and self-employ in Canada/Quebec. Self-employment, according to (I think) RQ is a moving target and is surprisingly hard to prove from my very superficial research in the area. I have a few friends here in Quebec that do contracting in IT. Without fail, each one formed their own company/corporation (with them, of course, as the sole owner/employee) and they billed corp-to-corp to the client company. They all have accountants that they use to keep the books legit.
One-off observation - Tax dude told me that, if you claim foreign income exemptions on Canadian taxes, CRA takes it very seriously and audit 100% of all claims. He could have been exaggerating, but I'm inclined to believe a guy that does this for a living (And I just paid money to for his advice), so I opted for the route less painful (i.e. - declining the offer)
Assuming you get a competent and not too pricey tax accountant, then I figure it's just a small cost of doing business. Very often, the US corp will pay you far more than most Canadian corps, that paying the accountant is a perfectly reasonable expense.