Some people here are misleading you!
1. You may need to file with Nebraska center/Montreal consulate. Contact a lawyer or query BCIS to make sure.
eg. http://www.americanlaw.com
2. You will get interview notice from Montreal consulate and this way will be much faster than I-485 filing.
3. Yes. Both L1/H1 work in this case. If you have already in the States, you may change back to I-485. For Canadian, consulate processing is a fast way over adjustment status. Even if you're in the U.S., you can still apply consulate visa processing as your last step to Green card.
If you become Canadian citizen you will also qualify TN status. A pending/approved I-140 itself and/or intent of consulate processing will not bar the renew/extention of TN, but an I-485 will.
Hope helpful!