The Swedish companies Volvo and Scania are two of the largest manufacturers of heavy trucks in Europe. Both are also making marine diesels and Scania mainly for commercial vessels. They have a good reputation in Sweden, where they have been produced for over a century now. About spare parts in the US, I guess you will have no problems even if it may take a couple of days to get them.
Yep, here in the Channel Islands we look after a number of Scania motors on the fast ferries and fishing boats. Not much goes wrong as they tend to be slow/medium speed marinised truck engines. Tough stuff.