I entered Canada on my American passport but so they my correct details would be sent to the EU, I checked in and used my Swedish passport when exiting Canada. Will this cause issues in terms of Canada thinking that me the American is still there and then overstaying?

Just save your boarding pass if it should be an issue.

Strictly speaking, Canada and USA do not have immigration exit controls.

Showing the passport to the airline as you are exiting Canada/USA to the next foreign destination is to show them that the next country will allow you entry by virtue of citizenship or visa.

If you define immigration exit control as stamping a passport then you are correct there is no control.

However there�s more going on at immigration than just stamping a passport such as tracking exit and preventing individuals wanted by authorities from departing.

Exit is tracked. From CBP perspective by air it is via APIS (CBSA has something similar), by land, via Exit/Entry agreement between CBP and CBSA.

It�s been documented that CBP will pull passenger off a departing flight due to APIS information submitted by the carrier matching person of interest. They can also do a money search on the departing jet bridge/land border.

Just because you don�t see a checkpoint doesn�t mean there are no immigration exit controls.

Let's say you enter by air into Canada. They scan your US passport. And you exit by land. The CBP agent just takes a look at your passport and waves you through.
How does Canada know you exited?

Phase 3 of Beyond the Border Action Plan implemented back in 2019.

An entry on the northern land border will be shared with the other border agency so they can note that as an exit.

CBP could have just RFID the passport.

So if you drive up across the border for duty free and come back before being out of country for the minimum duration to qualify for duty free exemption, don�t be surprised if they already know the answer to the question of how long were you in the other country before they even asked.

Many times at YYZ T3 I have precleared US immigration then my flight gets cancelled or I accept a VDB credit and I simply exit to the street. Canada has no clue I am still in Canada. Note that when this happens in T1 with AC I always have to reclear Canada Customs (because some travellers bypass entry to Canada while in transit). But never in T3. I often buy a dummy refundable ticket to see spouse or kid through US immigration and pretend I am travelling with them then I simply leave once they have boarded. The records show I am in USA but I never board the plane and just go back to my car parked at YYZ.

I think that would reconcile itself when carrier reports actual manifest to CBSA and CBP.

OK, but still how will it work when I use my old country's (EU and Schengen member) passport when traveling to the EU? EU will require ETIAS pre-authorization starting in Nov. 2023. As an EU citizen I'm not eligible for ETIAS. As a Canadian citizen I'm not eligible for eTA. So I'll indeed have to use my EU passport when leaving for the EU and my Canadian passport when returning. How will the authorities reconcile that?

Similar to an ongoing thread concerning US dual nationals where US regulations requires US citizen to bear US passport enter/depart US, present both passports to the airline and let them figure out their reporting requirements especially since you have no concerns about overstaying in Canada being a Canadian passport holder.

That has been extensively discussed in the Practical Travel Safety and Security Issues forum:

If you enter Canada on a US or Canadian passport, you shouldn't need to worry about having entry and exit records matching up because CBSA doesn't keep exit records for Canadian and American citizens (per https://www.cbsa-asfc.gc.ca/agency-a...r-rav-eng.html).

In general though, entering a country on one passport and leaving on another is a very common case, and most systems are set up to handle it. Most of the time entry and exit records are reconciles by passenger name and birthdate, not passport number or citizenship. As an example, I almost always enter the US on my Canadian passport and leave on my British one, and the entry/exit dates on my visitor records have always been correct. However, a colleague of mine who has a very common first and last name is often flagged because someone else with the same name and birthdate once overstayed.

Thanks!

I admit I didn�t ready every singe word in the link but it appears to say the exact opposite of what you indicated about exit records for CAN/USA citizens.
The 2019 date aligns with what I mentioned earlier about Phase 3 of Beyond the Border Action Plan.

I didn�t see anything about this exit information being purged after a period of time.

Indeed you're right, I misread the page. That's what I get for posting while jet lagged.
Given that almost all my trips involve entering Canada on my Canadian passport and leaving on my UK one, I've just put in a Privacy Act request for my entry and exit records to see if they do match them up the way the US does. It's too bad that they say it will take up to 30 days to process the request. You can get the US data online right away.