Toronto Canada to Corpus Christi have 25ft travel trailer

Look at the subscription website Boondockers Welcome for short stay opportunities on private property.

You won't need reservations for short stays.
Long stays in a decent park will be almost impossible to find. Look around and reserve for next year.

I will confine my remarks to the route within Texas as I am very familiar with these highways. I will assume a starting point of Texarkana, Texas.

Look for the US 59 exit from I-30 indicated "Houston"
@ Marshall take Loop 390 around Northwest of Town to TX 43
@ Henderson take US 79 (loop around Palestine) all the way to
Rockdale then take US 77
US 77 will take you all the way to the vicinity of Corpus Christi.

Good commercial campground at Shady Pines, Texarkana (bit out of the way)

Good State Parks at Caddo Lake and at Tyler, require small modifications in the route above.

Slight modification allows visit to Bryan/College Station and the George W. Bush Presidential Library.

I could give many other alternate routes, but this is one for a start.

I don't know about Florida, but there are a ton of campgrounds in Texas, so you'll always find a place to stay. But... you will definitely want to make reservations for something on the coast, or you will be stuck in a sketchy campground.

Looking to get out of frigid temps as quickly as possible on way down

Stay off the interstate system, you'll see more on the byways.

Thank you for your reply we are planning October 2019 thru 2020

Well I hope you have reservations for the cg you plan to use. That is the season down south and people make reservations a year in advance. I know you'll have a very hard time in Florida w/o locked in reservations and I'd guess it's the same in Texas. And on the gulf coast in between those locations.