in larger dogs which dog is the calmest and most easily trained

newfoundland or st b.

Opinions vary because of a definition problem on the term "larger".
Golden Retrievers are also generally considered very mild and eager to
learn.  Ditto for Bernese Mountain dog. And, the Black Lab/German
Shepherd 50/50 mix.

My problem is I don't know what dimensions mean large dog to you.  In
their extreme size category, the two previous suggestions are
certainly well known for their pleasant personalities.

If you do want a dog that large, do consider if you are going to have
enough room for them to be comfortable.

While not a direct answer to your question my wife found the following
invaluable when confirming her choice of dog...

http://sy.adiho.com/ASA/Controller?adi_hasScript=1&_AD_195R22=85&adi_scriptSID=08680A9DC1D8E9CD4545358DCA69A63C&sysid=4&appid=9901

It is a question/response form from Purina powered by Active Decisions
that really gets you to think about what you want from and can give to
a dog and gives you breed choices based on that.