I am a Malaysian passport holder with an American student visa. I have booked my air ticket on 29th May for travel from Portland, Oregon to Malaysia with transit in Vancouver. Only after my booking, I came to know that I need a Travel Without Visa. But the online application needs about 32 days...I have run out of time. Could I just go straight to the airport on that day and get the express "Travel Without Visa" document and pay the fine at the airport?
Apparently, you do need a transit visa and do not qualify for the transit without visa program (which is not a document but a regulation allowing some people to transit without any specific document beyond their passport) as it's not open to Malaysian citizens.
You should either change your flight or apply as soon as possible and hope the visa application is processed quickly. You also risk being denied boarding in the US and losing your ticket entirely as airline personnel should check your right to transit through Canada.
I don't know which “fine” you have in mind but fines are typically not intended to replace visas and you won't find any Canadian personnel to deal with this in Portland. US border agents cannot grant you the right to enter Canada so you will most likely be stuck there and never get to the point where you could pay a fine in Canada.