Legal entry from Canada

[Komodd]

Recently I've got Green Card Visa and untill October I have to get into USA as a permanent resident. I live in Toronto and nearest point of enrty is Buffalo. Can I get into USA at this point, fill up all application papers to get documents ( Social Security Number, Driver's licence, etc..) and return to Toronto waiting for this documents ( after I will give goverment office my Canada's address or it needs to give them any USA address?). After I will get this documents how long could I stay in Canada intill I will found job and rent appartment in USA?
Thanks in advance.