Is this a Mason Bee?

Hard telling from the picture. Mason bees are pretty small but Carpenter bees do burrow into wood and make nicely neat 3/8th inch holes. Carpenter bees are generally pretty big, looking much like a Bumble bee and their abdomens are pretty dark/black in color.

These are small the size of a honey bee maybe even slightly smaller.

We've always had carpenter bees here. These are definitely not carpenter bees

You are lucky. You might check out "Crown Bees" website and order a Mason bee house and some reeds and try to draw them to that instead of your barn. My location isn't right for mason bees but I am going to order some Leafcutter bees from Crown Bees about the time my garden is going strong. I had Carpenter bees mess up my little log cabin by the pond so I made traps for them and plugged the holes in the cabin logs.