My wife, who is Thai, will travel with me from Bangkok to Toronto. If we book a flight which stops in Japan, either just to change planes or requiring going to a second Japanese airport, what are the Japanese visa requirements for my wife?

She is visa exempt into Japan for, I think, 15 days. No issues with your plan.

9 hours ago, NewGuy said:

My wife, who is Thai, will travel with me from Bangkok to Toronto. If we book a flight which stops in Japan, either just to change planes or requiring going to a second Japanese airport, what are the Japanese visa requirements for my wife?

If she is just changing planes she won’t even pass immigration, just security and then onto shopping in the duty free area. Have her bring you some Yamazaki 12 whiskey