When we are strongly aiming for a long lasting alliance it is best to be as honest and open as possible. I like 2metra's second message. I'd say that's what we want to send. Subtlety and hinting at your true intentions are good if you have enough time to slowly build up mutual understanding. Or if you are not quite sure yet if you want to ally with a team you can try to prod them with carefully formed messages and then decide based on responses. With CP we know what we want and that is to ally with them. Thus, it is best to let them know it as soon as we meet them. Also, we want to know their stance as soon as possible since the direction of our strategy depends on their response.