No, technically, you don't have to leave the US to apply to Canada, but you do have to apply to the Canadian Embassy in your country of legal residence, if I remember correctly.

Search for my posts on my Canadian visa application process and you'll find my correspondence with the CICs in the Philippines and the US advising me to file my application with the CIC in Manila.

There are four former DREAMers who applied for a Canadian student visa that I know of. Here are their case summaries:

1) GrumpyDreamer- left the US and applied to the CIC in his country of origin (Philippines), was approved without having to do the interview, doing doctorate work now.

2) Beowulf- didn't leave the US, sent his application to a relative in his country of origin (Mexico) to have it processed at the CIC, was approved without having to do the interview, working on his MS now. He submitted recommendation letters from his previous professors and from the Mexican consul along with his application.

3) Moi- originally sent my application to the CIC in my country of origin (Philippines), returned for the interview and was denied, but life worked out for the best so whatevs, I'm still gonna get my PhD for free.

4) Alex1234- undergraduate, didn't leave the US, originally sent his application to the CIC in his country of origin (???) and was denied, reapplied to the CIC in Washington and was approved without having to do the interview.

There are a few more DREAMers who applied and were denied, but I can't remember who they are and I can't find their posts. Actually, make that I can't be assed to find their posts.