visa to enter Canada & visa to come back to the US

Chinese citizen holding a H1b in the USA. I will go to Canada for a conference for one week. I know I need a Canadian visit visa to enter Canada. My questions are:

1. How am i going to get back into the US after the conference? I think I need to apply for a USA H1b visa to come back to the USA, right?

2. When and where should I apply for the H1b then? (Do I have to apply for the H1b in Canada, say in Toronto, when the conference is taking place? Or I can apply for this H1b before I actually enter Canada?)

3. If I need to apply for a H1b in Canada to come back to the states, is it sufficient for me to do so within one week during the conference?