When I cross the US/Canada border, neither side stamps my passport. Does this mean that there is no record of border crossing in their system? Just curious.
Generally: If they do more than just look at your passport / ID then there probably is a record. The US records entry/exit data with the I94, partly electronically. In Canada, entries have been recorded for all travellers since 2000 and since 2019, exits are also collected on US and Canadian citizens.
I crossed with an Austrian passport from Seattle to Vancouver by rail in 2018 and didn't get stamps, but the border crossing was recorded electronically, at least for the US it was listed in my I94. I don't know if Canada has an equivalent record, but I left Canada by air, which may not have been recorded at the time.