Hi - yes. When we were there in July you could buy WiFi cards from reception for around £1.50 for a 1 hour card. You can use their computers or your own devise.
The internet is not widely available in Cuba and connection can be intermittent. You can access the WiFi from the main lobby and just outside along the patio area so you can enjoy a coffee or a cocktail while you’re there.
Get an answer from Sol Cayo Guillermo staff and past guests.