You can sponsor her from the Philippines while you are in the US. This would be an Outland Application.
Here is where the burden of proof is going to fall on you, though, as a sponsor outside Canada.
- The relationship is for real. everyone has to prove that, but the burden increases when both applicants (a) are not married (b) live apart (c) are outside of Canada and in different countries.
- That you, the sponsor, are serious about moving to Canada yourself. It's a big move. They will want to see that you have (a) thought it through (b) have started putting the pieces in place for the move.
It's not a problem. People prove those things to the CIC every day. But my guess is these are the questions the case officer will be interested in most.
Also - I agree with KBH: don't sponsor for the US just to turn around and sponsor for Canada. It'll add a year or two to the process, and could potentially make your application look less credible.
Good luck.