How do you know if you are considered a non resident alien if you live in canada (citizen)
And work in canada and US are married and have to file a us income tax?

For filing a US return how do you know what you are a non resident alien or resident alien if you have a L1B and are a married canadian citizen

Any income earned while in the U.S. must be reported on the U.S. tax return.
If you meet substantial presence test or you are filing joint return as residents, you must declare your worldwide income. Your U.S. Tax Return: Substantial Presence Test (http://taxipay.blogspot.com/2008/04/substantial-presence-test.html)