B2 transfer to H1-B?

I got an offer from a USA firm.. Right now I am in Canada and hold the Canadian green card. I also have a 10 year multi-entry visa to the States, last time I went to the USA for interview and got a I-94 valid through Feb. next year.

I am curious about the best way to apply for H1-B. Should I come first to the States using my valid I-94 as a visitor and then apply for B2 transfer to H1-B status? Or, should I apply for H1-B visa in Canada?

Can anyone suggest which way is better? Thanks a lot!