My experience for connecting flights to Europe is what's been mentioned so far. If you're travelling with the same airline on one ticket, your checked luggage should go directly to your final destination. You'll check it at your home airport and won't see it again until you arrive in Rome.
However on connecting flights from Europe, it's been my experience (numerous times) that checked luggage has to be retrieved at the first arrival airport in Canada, and then re-checked immediately for the next flight. That may have changed in the last year or two, but that's what I've found whenever I've transited Toronto, Calgary or Vancouver.
In terms of clearing Customs, you will have to go through a CBSA checkpoint first. As this website states, "If you are arriving on a US or international flight, you will need to confirm your identity with CBSA and declare any goods that you are bringing into the country"* - https://www.torontopearson.com/en/connections/customs-immigration .
United Airlines uses YYZ Terminal 1 for check-in, arrivals and departures, so that should will probably make the connection relatively easy. If you're flying direct from Toronto to Minneapolis, you may be using a code share airline (Air Canada, Delta)?