回复：同问：拿到第三国签证回美是否会纠缠开学前一定时间才能入境的

You raised a good question. But earliest time to apply a visa/or to use visa to enter also applies to the interview at the US consulate in Canada. You have the very same problem with the US Consular officers in Canada. So why are you only worrying about the re-entry to US but not worrying about visa rejection based on applying too early?