I believe Bryer's dad mentioned that they had discussed Bryer possibly going elsewhere to look for work in the recent past (not sure of the source on this, but I'm pretty sure I saw that). I know he also said that Bryer had cousins in Alberta and he assumed they were going there.
But it does sound like the plan to leave was pretty sudden. Kam's parents were likely aware of it at least a day or two beforehand since they gave them the truck and camper and I'm sure it took time to pack everything. Bryer's grandma and great-uncle were aware of it either on or before the 11th (in his great-uncle's interview with CBC, he said that he last saw Bryer in his grandma's car on the 11th and his grandma said Bryer would be leaving the next day).
I actually don't think it's that weird that Bryer didn't tell his dad until the last minute. As I've mentioned, I have a similar awkward situation with my own historically-absent dad, and he's kind of peripheral to my life, not in it. I don't tell him about a lot of stuff going on in my life. It is pretty inconsiderate that he didn't tell his dad until his dad was en route to visit him, but it's possible with all the preparations going on, he may have just forgotten that was the day of the month his dad usually visited, or something.
It is really weird that he told his dad they were going to Alberta though. Even if it was planned as a murder trip, it's weird. Why lie? If they were trying to get away with it, it would make more sense to have a consistent story to avoid suspicion. If it was planned as a suicide mission, why would he care if his dad knew where he was going?
The only explanation I can think of that makes any logical sense, is they had a couple of possible destinations in mind and hadn't decided on one yet.
That doesn't surprise me. In the 60 Minutes interview he was still in denial that Bryer killed anyone and said "I'll believe it when I see the evidence." Denial is a normal part of the grieving process. I'm sure he rationalized a lot of things, just like he rationalized the Nazi stuff even before this all happened.