Being in the US without visa/passport inhand

I am currently working in the US on a TN-Visa. When I got the visa I was told that I needed to keep it and my passport on me at all times. I have to travel for work and will be going to India in the next few months. In order to get a visa to travel to India, I have to send in my passport and likely wont get it back for 2-weeks. I have a nexus card, is it ok for me to remain in the US with just my nexus card? I could take my I-94 out of my passport before sending it in. Will I be able to go to Canada and back with just my nexus and I-94?

You should NOT let your I-94 leave you.

call nexus to find out if you can cross with card only. I doubt it, especially by air.