Any Newfie owners out there - especially psychiatric service Newfies?

[Ms. Toad]

My daughter is the proud owner of a 2-year old 110 lb Newfie/Pyrenees cross. He appears to have inherited most of the Newfie traits (extremely people-centered, constantly sniffing everything, very bright, largely quiet, not nocturnal). His prior owner was a "let the dog be a dog" type, so not much formal training.

Until he's trained as her service dog, and can go to work with her, I'm walking him 4 days a week while she's at work and helping out with training. (She has C-PTSD, and expects to use him to alert her when she's winding up emotionally, and to help her focus on calming down before she does/says something to get herself fired.) He's learned go to crate, sit, stay, (hand me your) paw, down - reliably indoors with only 4 cats to distract him; starting to work on extending them outdoors. Informally, he is very good about stopping on the dog blanket when we come in while I clean the snowballs from between his toes, and dry off his feathers. He recognizes my car lock chime from across the street - and lets out a few woofs as I walk to the steps. (Also when I leave). My daughter is working with a trainer - first on good citizenship stuff, then on service dog stuff.

Challenges so far:

Leash manners. His prior owner used a prong collar on him (all the time), and controlled him just by pulling on the collar - so he's used to forcefully (and uncomfortably) being brought to attention while walking - rather than keeping track of where his person is because that is what is expected of him. As a service dog, he'll need good leash manner - and will need to be attentive to my daughter. So far, he's too distracted by the wonderful smells of anything and everything to stop and pay attention to the silly human attached to his leash. (Manners aren't horrible - most of the time he walks on a slack 10' leash. He's just not checking in, or paying attention to make sure he's not too far ahead. The only problem - as a pet - is that he's 110 lbs and he loves to meet other people and other dogs, even if they don't want to be greeted. If I grab his harness, he will stand next to me, but if I don't have his harness he could easily overwhelm the person/dog. And as a service dog, he needs even better manners.)

Car anxiety. His prior owner rarely took him anywhere by car. We picked him up a state away from us, and drove him 3.5 hours away from the only family he has known, after a single meeting. (Wife apparently wasn't aware of how big he would get - and just wanted him gone now that he's full grown). I think it's that combination that has caused his extreme car anxiety. He's adapted well (to the extent we can tell) - emotionally connected to both my daughter and me, playing with toys, eating well, no acting out. But he will have to be able to travel by car without the effort it now takes to get him into the car.

I'd love any tips anyone has on teaching a nose-focused newfie to be attentive to his human (including creative things we can do when we're not training to satiate his glorious nose), and on lessening car anxiety.