Hi Scottish. You were able to relate how you feel about your brother, his fiance, and this marriage very well here. I think you will do fine with your speech.
You may want to forget about the "canned jokes". Most of the better best man speeches are from the heart and relate funny personal stories (nothing that will cause anyone there any embarrassment). Talk about something funny that occurred with either the bride or groom, or both together. All you really need is one good funny story. The best way to begin writing this kind of speech is to start a journal. Write down funny stories from your childhood that you remember which involved your brother. Think about your brothers good qualities and jot those down. Think about the qualities of his bride-to-be that make you feel love for her, and jot those down. If something funny happened while they were together as a couple, that would be a great one to tell, so write it down. Write down the things that either one of them did that made you feel proud to know them. Write down the things they have done as a couple that impressed you. They way they look at each other, the way they interact, they way they treat others.
Your speech doesn't have to be long. Once you have a few good stories to refer to, start thinking about which stories are the most appropriate to the occasion. Here is a good reference guide to give you the do's and don'ts of a best man speech.
Giving a Best Man Speech - The Do's and Don'ts of Giving a Best Man Speech, and an Example to Start You Off
Here are some sample speeches that should help you as a guideline of how to put it together:
Best Man Speech | Free Best Man Speeches | Free Samples
Free Best Man Speeches
Best man speeches and best man speech material
I hope this helps you get started. When you eventually write your speech, if you want to post it here for some help with fine tuning it, you know you will get a lot of input from people here. :)
