i have a saint and she didn't chill out until we had ds, 7 months ago. she packed on her last 20 lbs or so last september and that seemed to mark the beginning of the change into adulthood.
big dogs can still be very energetic. we used to joke we weren't tiring zocha out, we were building her stamina.

for visitors, we're still working on making her sit and wait. we always physically block her way to them so we don't freak people out. except for the people we don't like.

but we are always very strict with her to make sure she stays gentle. she has to sit for kids and other dogs. if the seem interested but wary we make her lay. if she gets over excited at the run, over she goes on her back. she MUST show her belly until we release her. i usually even put my foot on her chest lightly to reinforce my dominance. quite the sight when i was full term w/ds. we also do that with visitors she loves so she doesn't bum rush them to get pet.
we've found a very firm, gentle hand is best. and addressing corrections immediately. they are stubborn and smart as hell. i think newfies have the same temperament.i never used treats, but dh did. good luck! (for jumping, we NEVER allow it. knee/heel of hand to the chest, push them down with a firm,sharp NO! followed by DOWN)
beautiful pup!