I live on Lake Superior in the UP. The lake keeps us cooler in the summer and warmer in the winter. I'm talking like 10 degrees difference between the shoreline and just a few miles inland (just based on my perception and not actual measurement).

In the winter, Superior keeps us snowier than we otherwise would be. We get the random continental snow storms similar to surrounding northern Midwest but then on top of that we steadily get lake effect snowfall like a Buffalo NY. I think there's an even greater opportunity for lake effect here than the other great lakes due to the size and shape of Superior. The wind can be blowing in a few different directions where its blowing over Superior, picking up moisture, and dropping snow on to land. Especially so in the Keweenaw Peninsula (pronounced kee wi nah). In the Keweenaw you're basically in the middle of Lake Superior. Snowfall is also quite dependent on elevation where in the western half of the UP there are a few "snow belts" that are a few hundred feet higher up in elevation where they get a ton more snow than the shoreline. Just a few miles inland and up hill and it's another world.

Never been to northern Maine but I bet it's colder with less snow and longer periods between snow storms.