It may have been high considered high based on the locals' technology and general lack of any sailing ability but by 1750 (the earliest data I could find) the population was about 150,000. Depending on when the colony is settled I'd expect we'd get nearer to those number far sooner, possibly in the 14 or 1500's. Looking at Majorca which had stable a population of ~97,000 between 1580 and 1670 I would expect the Canaries to support at least that many since the islands are double in size.
Also the Canaries were an exporter of high quality wines and dyes for a long time (and then later sugar) so there is at least some resources
That's what i'm trying to get at, sugar cultivation (not sure wines would be that profitable to them at this point, unsure about the dye industry) would be introduced with settlement, so the canaries and sicily would serve as alternate sources of sugar for europe when the near east is lost. Arguably ships capable of reaching the canaries should be able the skirt the african coast maybe up to the mouth of the senegal river if not further and up to Iberia maybe the atlantic coast of france. I don't see them forming permanent settlements in more sub-saharan africa but they might be able to form a profitable alternate trade route for W/African peppers, gold and Ivory to europe as opposed to the land route.
I'm thinking the islamic empires at the time would have little incentive to take over the islands as the main route with the bulk of goods will still be via the sahara. On maintaining links to christian europe especially prior to the reconquista during the islamic golden era, i think the most difficult part might be the 40yr era of Umayyad iberia from 710ish to 750ish as Korpulu alluded to earlier.
We could possibly see syncretic forms of the byzantine rite in some parts of w/africa and if successful enough large swaths, I also recognise that given the era trading in slaves would likely occur but I'm going in with the mindset that earlier exposures to trading with europeans via the canaries leads to cultural and technological (especially tech, less interested in the cultural) exchanges that would disincetivise the practice of exporting slaves (use them in your own territories to maintain your empires, eventually abolish the practice when no longer profitable). The byzatine/berber canaries & europe may see sub-saharan africans as allies against incursions from the arabs, hire them as mercenaries, form alliances etc encouraging technology exchanges.
We could potentially see
- earlier introduction of different forms of weaponry (armoured suits not helpful, but sturdier lances)
- writing system as an alternative to the islamic script or development of indigenous writing scripts with byzantine influence
- more w/african empires & polities like Mali, possibly earlier or stabilising of earlier polities like Ghana empire in the region. Basis of this is the introduction of horses strengthened regional players like the caliphates of now Northern Nigeria and the Oyo. W/Africa isn't that suitable to horses actually because of disease but earlier introductions with a stable supply would lead to earlier spread and devt of local strains more resistant to disease. The lessens pressure to trade people for horses (a factor in the slave trade)
-earlier introduction of gunpowder later on.
This is a rosy picture I'm painting so do critique but I hope you'll also be open minded.