The radio only loads what you have geographically selected (by way of your location and range).
If it is trying to load Canadian data on boot-up, you can lock out (avoid) or deselect those items and it should help the boot speed, but deleting them from the DB is just a chore that is going to tire you out, having to do it every week after the Monday database update. In other words, it's not worth it.
In Sentinel, go into Canada, then Ontario (I'm wagering from your published location that you're encountering stuff from south-western Ontario), and then drill down into each "county" you are receiving - this is the difficult part, unfortunately you cannot avoid an entire state/province.
You're probably dealing with Essex, Chatham-Kent, Waterloo, Lambton, and Middlesex; and maybe Huron, Perth, and Wellington and Bruce. Go into each of those, into the County Systems, highlight them all, and press Ctrl+L to avoid ("Lock out") each one. Also do this for "Statewide" (but you will only have to do this once, in the first "county" you go into).
These avoids will stay permanently in your Sentinel settings, not erased by database updates.
I use a similar process to keep British Columbia comms from entering my scan list.