You find them the same way you would any regular job: apply at the companies that interest you for a position you're qualified for. They'll be advertizing the jobs on Canadian job boards (monster.ca, workopolis.ca, etc) or they'll have the job description posted on their website. Hiring outside of Canada and sponsoring a foreign worker for the vacant position would likely be the company's plan B or last resort. Legally, all Canadian companies have to prove that they advertized the position in Canada and that no Canadian applicant was qualified enough before they can apply to sponsor a foreign worker to fill the position. What I'm saying is that you won't find career opportunities specifically advertizing that they're recruiting foreign workers only
. Of course, that doesn't mean that foreign workers can't apply.
If you're the most qualified individual, there is a chance, right?
Generally companies looking to hire international workers are companies which need to fill very specific positions... an example of this would be highly skilled technical positions in health care/IT... positions that are tough to fill due to the lack of truly qualified individuals. Or a different situation which is very common here in Vancouver is work in the video game industry. If you're an established video game producer, 3D artist, art director, programmer, animator, cinematographer, etc - start applying at all video game companies, pronto!
EA (major video game company) for example, hires many people from abroad - they will bring in top of the line talent from anywhere. But by top of the line, I mean people who have worked on big name titles (ie: Lord of the Rings, the CSI series, etc) who have worked with the top of the line talent. EA will eat that up and will fly you in from around the world to work for them in Canada if you have those skills.
I guess my point is, the question is not "where do I find companies looking to sponsor foreign workers", but "do you posess a highly sought-after skill that is in demand in Canada?"
Customer service/retail/high school teaching/administration/finance/etc, would not be considered in-demand positions.
Specialized doctors, specialized IT gurus, university professors in niche fields, professional artists in film/TV/video games, etc - they would be more likely get sponsored (assuming there is a position for them).
Of course, this is all generalizations, but since I don't know what field you work in, it's hard for me to say.
Just start looking at job boards and start searching the employment pages on company websites. Apply - you never know.
Also, one interesting blog I've stumbled across is called "We Move to Canada", about a couple from New York who decided to move to Canada. You can go all the way back to their first posts in 2004 and follow along their journey to Canada: we move to canada