It depends on the specifics of your situation. Both are transparent entities.
However:
1. US LLCs are required to file with the taxman, while Ontario LP seemingly not
2. The US filing requirements have been set up with the explicit intention of information sharing with other countries ... though apparently not being done ... yet.
3. US LLC might be able to open bank accounts in the US, while the Ontario LP is unlikely to achieve same in Canada.
4. Canada LP lower profile than your standard Delaware LLC