When I did our flyers, I started with "Northern border states", but was told that most Americans assume Mexican/US border when you say "border states."
Canada is WAAAAY 'wider' than the "continental" USA [still think that's a weird term], since we already included "Canada" as a range, and we're likely to be doing at least one presentation in the Maritimes, it seemed appropriate to include side-trips into the US either on the way there or on the way home. So, yes, we're certainly planning on travelling considerably more than your suggested "within 300 miles of..."
In case anyone's wondering: thus far we've got a solid booking in Ucluelet [I'll let you look that one up...gorgeous place!], and inquiries in Chemainus, Richmond BC, Kelowna, Calgary, Saskatoon, Haliburton [Ontario] Baltimore [New Brunswick], and possibly Vermont. There's a geography lesson for you!