University of Toronto admission questions

Hello, I am an American student looking to apply to U of T and have some questions…

Ive heard many different things on which grades they look at as Ive heard 11-12, just 12, just 11, and all 4 years and I have no idea which is it?

I did terrible freshman and sophomore year, but great Junior and Senior.

Also do they receive my GPA for all 4 cum years or the Average of the last two?

They don’t look at 9th and 10th grades. Your school sends in your full transcript - but more than once. Here’s what the schedule was for 2016 admits:
Sent to OUAC beginning Monday, October 5, 2015
Sent to OUAC beginning Monday, January 25, 2016
Sent to OUAC beginning Monday, March 14, 2016
Sent to OUAC beginning Wednesday, June 1, 2016

If the October transcript is stellar, U of T may offer admission around the end of December based on 11th grade marks - this is very rare though. If the transcript with 11th and 12th grade marks, received the end of January is excellent, they may offer admission the first week of February. Otherwise, admissions will go out in waves in March and May, based on 12th grade marks. Which transcript is used/when the offer is made also depends on when your 12th grade English and, if applicable, Precalculus and Calculus marks show up. The sooner and better those marks are, the sooner you can expect an offer.