Re-entry on H1/H4 after different lengths of time

I'm told that I should not surrender my I-94 when going back to Canada for a short (1 week) visit. If I go back to Canada for an entire summer, though, I do surrender my I-94.

1) What differences are there in the documents I need to come back to the US for a short visit vs. a longer (2-3 month) visit to Canada?

2) Also, can an H1B or H4 person work for a summer inside Canada (for a Canadian or US consulting gig who is NOT their H1B employer) without threatening their US status? I don't know if your activities once you step onto soil outside the US matter to your status.

1) There is never a "need" to surrender your I-94 if your status continues to be valid. The officer, upon your return to US will decide whether to issue you a new I-94 or allow you to keep the old one. Thequestion becomes whether leaving US for so long means that you are no longer employed.

2. In H1, you are required to be an employee of the sponsor, and are to work and be paid by the conditions of your LCA. So, unless you are on vacation, your H1 ends, and must be revived when you return to US. To be "benched" by your employer invalidates your H1. But if the H1 remains vaild, it doesn't matter what you do outside US.