What about a surviving independent Breton state that, sharing a land border with the much more powerful French monarchy, pulled a Portugal and turned to the sea, conquering and colonizing vast chunks of Africa, the Americas and Asia, or a hypothetical independent Irish state doing the same to avoid being gobbled up by England?
The bretons seem to be quite likely as alternate discoverers of Northern America because of their interest in cod fishing, but an Asian colonial empire seems quite more difficult.
Ireland is also favoured by a big population surplus in vast tracts of its history. I am all for something like an irish-welsh "celtic" colonial power.