Having I485 pending, at the same time landing in Canada raises questions to many Americans including IO. If you landed before I485 filed, it is different. You are allowed to change your mind.
Even with H1 you are not guarteened to be safe
I saw one example. The person was stopped at the border and I485 revoked. The IO even put fraud on the note and sent to the consulate where he was supposed to apply for h1 visa cause AP was taken away earlier.