Late to the party but it might help someone else. As said above. Same way anyone would. Be it cis girl, or guy, or anyone. As long as your dog partner is mature and interested in sexual activities, it should be quite simple to get the right mood on. Get playful with him, play fetch, cuddle, play game of tug, whatever makes both of you excited and playful. From that it's not that big of a step to getting mounted. There are some more better guides here, if you need one.
He is really unlikely to mind that he is having anal sex (assuming you're not after op). As for you, just make sure to prepare. Get clean, and perhaps practice on some toys, preferably inflatable ones. He will stretch inside you and it will be quite a lot, so be sure that you are comfortable with it, because once you are anally knotted, chickening away will be painful. Also, try to keep him calm, you don't want him to make some sudden moves and literarly rip it out of you.
Be safe and enjoy