In an essay, I wrote"Immigration to Canada has taught me a lot." But my teacher asked me to use Immigrating to Canada..."I don't know why.What's the difference between them?
Hi yesite, welcome to the forums!

Immigration to Canada = All the people who immigrate to Canada, Canada's immigration.

So your sentence might be like saying:

"Studying Canada's immigration statistics, has taught me a lot"
Yes. When you say "immigration," you are referring to the general concept. When you say "immigrating," you are referring to what you yourself did.