Re: Madeira or Canaries?
I wouldn't assume that there will be more space in Madeira. Madeira has Funchal which gets really full to bursting and there is another marina on the adjacent island (senior moment here) but that's it.
The Canaries have a bevvy of marinas and good transport links back to most places. It is true that Gran Canaria gets a bit full but the other islands aren't so bad. You can also book ahead, we were in Puerto Mogan in GC for September havnig booked ahead.
"The best are indifferent, the worst are passionate advocates" WB Yeats