Sorry to hear about Canelo’s start in life. It’s early enough in his life for him to be rehabilitated successfully.
A puppy will be easier to ‘control’ than a rabbit in this situation.
You should be in charge of the meeting and should prevent rabbit and dog getting too close to each other.
It’s not obligatory that they become best friends, but that they just ignore each other when the other is around. Anything friendlier will be a bonus.
Unfortunately rabbit now knows he is safer in your arms and pup knows if he chases, bun will run ! There’s nothing more inticing than a chase for a dog !!
If dog is alert, ears forward and in “yumyum” mode just by looking (staring/drooling) at rabbit through the bars, say “no”, until he relaxes or drops eye contact and moves away. If he can’t hear you as he’s so concentrated, touch him slightly on his side in a Cesar Millan way.
Remember, consistant “rules, boundaries and limitations”… if you give him complete freedom to run wild, chase buns and not listen to you it could be dangerous for him and (very) tedious for you.
Keep them safely apart without tension for a while – a week is not long for a puppy to get used to his surroundings. Give Canelo lots of love, but only when you decide. If he is requesting it and whining, then ignore him or he will think he is the deciding boss, which will not only stress him out when he’s not in control but may also make him agressive when he’s not getting it.
My dog was abused and became ‘defensive agressive’ which meant when she felt threatened (by whatever!!) she would bark agressively rather than fleeing or welcoming it. When I “took charge” immediately by saying “it’s OK I’ve got it” then she relaxed completely like “phewie, thank goodness you’re here”.
A 5 month old abused puppy will rely on you to gently teach him right from wrong (like his mum would) and to find his natural instincts.
It’s so important for you now (and before 8 months) to introduce him to everything and anybody you can so he doesn’t create his own phobias.
Another tip to help an abused dog who has his tail between his legs, is when you’re stroking him, gently but firmly, on his back go all the way to the base of his tail, push it up gently (palm upwards under the tail) so the tail is in its ‘normal up’ position….. the dog will feel more confident – a bit like telling someone to stand up straight, shoulders back, chest out !! LOL
Good luck – but don’t force a friendship or it could be ruined for a long long time (not to mention injuries)
One step at a time – Lucky pup to have found you. :o)