thank you everyone for all of the great information ! , I have decided to ditch the CB radio idea and go with a VHF/UHF mobile setup . I'm looking at a Anytone 779UV . I'm hearing that GMRS is the "new cb radio" these days and there is lots of highway/interstate usage in the USA . plus up here in Canada most truckers use the LADD and RR channels on VHF .
GMRS/FRS does get used for car to car for people caravanning, and in some places you'll occasionally hear radio traffic on major interstates.
However, GMRS/FRS being FM, it is -extremely- common for users to have CTCSS/DCS set. A lot of the consumer radios come with it already activated. Because of that, it's not very common to have random conversations with those along the highways. GMRS is just not well suited for that. People want them for family communications, and usually are not setting them up in such a way that they'd hear a random person calling.
Also, most of the users you'll find are using hand held radios inside the vehicle, which gives them very poor range. Very rare to see anyone that takes the time to put an external antenna on.
It might be interesting to listen to, but random contacts like the old days of CB are not common.
Keep in mind that GMRS requires an FCC license in the USA.
In Canada, the GMRS service is limited to 2 watts, non-removeable antenna.
If you really want to listen to GMRS on your trip, a basic scanner will do what you need and cost less. Plus, it'll let you hear the LADD channels in Canada.