Later, and much larger, rounds of funding that is entirely unheard of in Canada.
Also, talent. This might be inflammatory, but I venture that the bulk of Canada's A-talent is already in the USA. Given the ease of the TN visa, I think it's not a stretch to say that if you're offering $70K for software engineers in Toronto, you are not hiring any of Canada's top talent, because they're all in the US making $150K+.
In my experience the few talented people who remain do so out of philosophical or family-related reasons, and that's a tiny, tiny slice of the overall pie.
> "I think that movement is changing.."
As a Canadian expat in the US I disagree. In fact, if anything, in recent years the brain drain of software talent from Canada to the US has increased as the software industry heats up down south. If your top players are consistently moving out of the country, it doesn't matter what government programs exist, you've already lost.
Talent is 95% of the problem. So long as US companies are offering fresh graduates $120K+ comp packages to live in sunny California, and Canadian firms have trouble ponying up more than $60K, the brain drain will continue, and Canada will continue to be scraping the bones of its own talent pool.