[vid]

The MTO has referred to the QEW as "Highway 1" or "Highway 451" but it doesn't have any official number, and Ontario has never officially had a Highway 1. The QEW through Halton, Peel and Toronto was Highway 2 until the 1950s, and part of the 401 was Highway 2A. Highway 401 was given its number because it was the second freeway to open after Highway 400. There isn't much logic to the highway numbering here. Highways 9, 10, 11, 12, 14, 15 and 16 are in order from west to east but otherwise, there is no logic. (There is no highway 13.)

2 - 148 are provincial trunk highways
400 to 427 and the QEW are provincial freeways
500 to 699 are secondary highways in the north
800 to 811 are tertiary highways in the north
Highways in the 7000 series are unmarked, and used for internal purposes at the MTO

I think they're numbered in the order they opened? I am pretty sure every other province (except maybe BC) has some sort of geographic basis to highway numbering.