You should use "may"because you are talking about something which is not certain.Can would mean that you are able to come.Here you want to express doubt.

Either. It depends on the situation. If I have the time... (and this is something I do not yet know) .... I CAN come to see you. So if I find I DO have the time then I definitely CAN come to see you. (can - means it is possible to do so now - and presumably I will go to see you) If I have time tomorrow, I can book you in for a check-up. (says my doctor) If I have 30 minutes spare tomorrow, I can chat on the phone with you. (So we wait to see if I have time) I may/might come and see you tomorrow, if I have time..... (well, I might or might not have time/ I might go and visit you, or I might not. Even if I do have time I might not!) I might teach the class tomorrow, if I have time. (This leaves everybody wondering about whether you are going to turn up at all!!) I CAN teach the class tomorrow, if I have time. (This gives everyone a little more hope. Provided time is available, it's possible for me to do it. My tone of voice will tell the listener how willing I am to teach.) If I have time tomorrow, yes, I definitely CAN teach the class tomorrow. I'll let you know later. See you then, I hope. If I have time tomorrow, yes, I definitely might teach the class. Let me see how I feel about it tomorrow. I may have a party to go to instead. Bye. (|This is not very satisfactory from the point of view of the school principal who is trying to arrange teaching cover!) Can you see the difference?

I might come and see you tomorrow if I have time. Might is the past tense form of may. We use it to express (50-60%) uncertainty, like maybe, maybe not. For example, if it gets cloudy outside, you could say, "It might rain." If you got invited to a party, but aren't sure if you'll go "Maybe I'll go" is the same as "I might go" If you got hurt and go to the doctor "you might need surgery", means that you'll possibly need surgery, but he's not sure yet.

Another example: If you go to Switzerland, you can go climbing. (Goody! A possibility!) If you go to Switzerland, you may go climbing. (permission OR uncertainty/maybe - depends who's saying it) If you go to Switzerland, you might go climbing (uncertainty/may you will/won' t or even a suggestion)

I've answered, but there are other examples: If you're tired later, you can go to bed (suggestion/possibility). If you're tired later, you may go to bed. (permission. If you're tired later, you might go to bed, (this is what I guess that maybe you will do!)