I have listened, quite entertaining especially when mom/dad has a backseat full of hungry kids ! You'll have to be very close to the burger joint though, preferably in the parking lot because they are low power radios. For freqs just use TAFL and enter the joint of choice, McDonalds, Tim Hortons etc....
I personally have heard Timmys on 469.0125, 902.2, 902.3. Coffee Time on 903.000 to name a few. Frequencies will vary from store to store, so it's best to use your search mode. Try searching 902-928 - you will find most of them there. Also 457s, 469s will get you some results too. Also try checking the 30 - 33 MHz band - some stores may be still using this band.
Years ago I would monitor a local McDonald's who used 30.58 for drive-thru comms. The range was surprising good as I could receive them about 3-4 km away.