From soemone who has spent tons of time doing various transborder routes several times a year, midsize or smaller Us cities to anywhere in Canada can be pricey. Add the ‘sold out summer’, or whatever they are calling it today, the fact that Canadian routes are not in particular are not back to pre-pandemic capacity, makes it worse. If you fly from an airport with more competition - say NYC-area or ORD, you are going to be a lot better off. Back in the day, when only DL was flying CVG-YYZ nonstop - there were a ton of trips where I paid $600-$700 several weeks in advance, even connecting on UA. This was in the late 2000s and early 2010s, IIRC.

Havent tried this recently, but in the not that distant past, the UA site didn’t always check married segment availability when confirming multi-city searches, so you could sometimes (but not always) get a better deal by searching for, say, ORF-ORD-YOW multicity vs. ORF-YOW. Try that with any connecting hubs that are available.

Also, particularly for Canada, one ‘trick’ I learned to use several years ago was to book separate one-way tickets vs. round trips. This started being cheaper when tickets typically became half the price of a RT for one-way. It’s not always the case on every route, but is definitely more typical than not for within North America now. For domestic flights, this typically gives you two one-way tickets that are the same price as the round trip. For Canada, this results in a lower overall fare. My understanding is it’s mostly to do with taxes - I am under the impression that Canadian HST applies to the total price of a US-Canada round trip, but only to the ex-Canada direction if a one-way. I’m not sure if there are other reasons as well, but I’ve noticed this has saved me about $25-$30/person per trip. Not a ton, especially on a $700 ticket If that’s what you are seeing, but when traveling with a family of 4, it adds up. Also, it will probably save more on higher fares - while many ticket fees/taxes are flat - TSA fee, CBP fees on inBound to US, AIF, etc., HST is a percentage, so cutting the amount of fare it is charged on by more is going to reduce it more.

as already mentioned, being flexible can also help - booking off-peak days/times/flights will probably help even more.