You won't be able to get to the transboder gates, you need to go to the domestic section. Your boarding pass has ITD OSS so you won't have to go pick up your bag, just follow the signs for domestic connections with Air Canada, and there's staff there to route people to the small CBSA booth. There are screens along the walkway to show you what gate you need.
You will definitely need the D Gates no matter what for a domestic flight. If memory serves, E is international, F is transborder, and some gates are E/F combos.
Keep an eye on the link from Pearson departures as this is likely the most up to date source of information.
https://www.torontopearson.com/en/de...7aca125yyzyvr/
well that’s annoying. I re-looked at this AC app like a dozen times and I can’t find any letters for gates in it.