This is such a great question! While it's different for all dogs, I'd like to make a few suggestions:

1) I think Daniel's suggestion of giving them their own space is a great idea! It might also be a good idea to try to introduce the dogs while one is kenneled so that you can avoid the risk of any unwanted contact, like letting the collie in the room while the great dane is kenneled or vice versa. This might help break the ice and help with the great dane's excitability. Once they don't seem overly interested in each other I would.. 2) Slowly introduce them with supervised play, but try not to limit their contact too much. If the great dane isn't aggressive and the collie is used to "correcting" unwanted behavior, they will eventually work it out. Like you said in your post, sometimes holding them back can create a more aggressive reaction. You could even try to standing between them to start out - make sure you have distractions for them too, like toys and treats! This will take the focal point off of the other dog in the room. Be prepared for a fight, but try not to be tense and trust that they won't hurt each other. Dogs can read tension and anxiety. 3) Trust that even if they don't like each other, they will eventually learn to coexist pleasantly. My dogs don't love each other, but they're both really happy dogs who do their own thing and even cuddle sometimes!

I hope this helps! One of my dogs is extremely temperamental and it's helped me to learn that there isn't a one size fits all solution for anything. Let them work it out in their own way, encourage positive interactions, and be conscious of their body language so that you can adjust how you see fit.