Was that the only scene?
Where the dog was forced to do something it didn't wanna do? I doubt it. If the dog showed resistance doing something, why not just use CGI? Tons of animal movies these days use CGI. It looked like a feel good movie, but now knowing what went on behind the scenes, it'll probably be hard to watch.
"It'll calm down once it goes in the water."
And when the dog goes under, "Cut it!"
Clearly it didn't calm down. They easily could have used a cgi dog for difficult scenes but they chose to use a real one.