Congratulations on the new addition!
I'm familiar with your off-leash park in Oshawa and you are right to avoid taking your puppy there until he/she is older. I take my weim there and he just loves it (you are so lucky to have that beautiful park). I do not take my papillon as some of the dogs get pretty boisterous and can unintentionally hurt the little ones.
Maybe make a few visits to Harmony Valley and ask around some of the owners advice on their vet experiences would be a good start. I found the park to be great socializing time for both me and my dog
FYI if you are on or near the Whitby/Oshawa border, I would highly recommend Dr. Kathy Kivi @ the Brooklin Vet Hospital on HWY 7 & Thickson.