You shouldn't have to "re-pair" the speaker. Once the bluetooth speaker is paired with your Macbook, it should reconnect automatically in the future. Waking the computer from sleep mode shouldn't be causing issues.
That said, stating how something is supposed to work isn't much help when, for whatever reason, it isn't working that way, so here's a possible workaround:
There's an Applescript on Stackoverflow here that will automatically pair a specific bluetooth device when run. You can save this script as an automator action, and then map the automator action to a specific keyboard shortcut. That way, you'll be able to pair the speaker with a quick keystroke whenever it gets disconnected.