I think you cannot have 2 valid visas at same time. So, once you stepped out of USA you need to schedule h1b apppointment to change your visa status. unless you have h1b appointment scheduled its risky. you can travel to canada or mexico with expired stamping and valid 797 for 30 days(AVR) but...
if you are sending from different courier it has to be 360 University Ave for drop box but canada post will give 225 simone st and technically both are same building so I hope nothing wrong here.