help need on AP and H1b

My current visa status is O1 and it will expire on March31 this year. My 140 has been approved last August, and I filed 485 latter last year.I need to attend a conference in Canada this summer, it is hard for me to obtain AP by then. My questions are:
1) If I apply H1b visa and if it get approved, Do I need to apply US visa in Canada to come back? see, if i only stay one week in Canada.
2) As I already filed I 485, will it affect my I 485 application if I change O1 to H1B?
4) If I file H1b petition, and could not get it approved by March 31, can I use EAD before get H1B?
Thanks

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• 回复：help need on AP and H1b -immigrate- ♀ (304 bytes) () 03/03/2004 postreply 12:15:30