Arnold had a small shop in Waltham across Woerd Avenue from the Waltham Canoe Co. and right on the Charles River. It was near the Waltham Watch Factory. Although Arnold was apparently a prolific builder, and many canoes seem to be attributed to him, your canoe is one of very, very few I have seen with a builder's tag. It would be nice if you could share more photos and document any serial numbers and formats etc.
If you search on "Arnold" or "Charles River" you will find more info on this Forum.
Fitz