Canon is irrelevant. As the film shows, the story could have easily been written so that Goku could fight the Red Ribbon army without any training from Roshi and not be killed. So, it's not necessary for him to train with Roshi first at all.And they could make a story that starts with Frieza landing next to his house and have him be defeated by kid Goku, which means it is not necessary for Goku to train at all.