I've cycled the Atlantic Coast (Key West to Halifax, NS) and the Pacific Coast (Vancouver to Tijuana). My impression:

1. There seems to be more temperature variation in the East Coast and hence harder to synchronize ideal time. When I did the East Coast, I actually did it as a sequence of shorter trips all in one year: Key West to Savannah, Savannah to Atlantic City, Atlantic City to Boston, Boston to Halifax. This let me enjoy the Maine Coast (beautiful) at the right time of year, while also visiting FL/GA/SC/NC at times that weren't too hot. If you are intent on seeing the Atlantic - particularly mid-summer, I'd suggest an alternative of starting in New York or Boston and heading north to catch the last bit of US Atlantic and then see the Canadian Atlantic Provinces and/or parts of Quebec/Gaspe Peninsula.

2. Parts of the Pacific Coast I enjoyed the most were between Astoria and Pismo, Beach CA. After that it became a bit urban for my preference though still some ok cycling. There are some parts of the Atlantic I really enjoyed (e.g. Outer Banks, Coast of Maine - particularly past Bangor) though it was a bit more hit and miss.

So my opinion is if you are intent on cycling an entire coast (Atlantic or Pacific) then despite having seen more of the Pacific, I'd still have a preference there. However, if your intent is in seeing new areas along the Atlantic, then I'd suggest altering the Florida to Maine aspect to instead look for Maine/New Brunswick/Nova Scotia/PEI/Newfoundland/Eastern Quebec instead.