I agree, while it may take some time after meeting her for him to change, I believe that it is better if we never give him the chance to do so. He already messed up our plans with just the Lancelot, I don't want to see what he can do as a Solar as well.
I think Suzaku would be more likely to Exalt as a Lunar than a Solar. When he ultimately came up with something approaching a plan to actually help the Japanese people, it was "become Knight of One so I can get declared in charge of Area 11 so I can take care of them". Seems more a stewardship motivation than anything else.
Also, Suzaku is more of a follower than a leader. Yeah, he's a great warrior, but a leader of men he is not. At best he inspires by example, but even with that he doesn't get a lot of hero worship. He seems to drift from master to master until the end of the series, and even after he takes on Zero's mantle he's ultimately following Lelouch's plan and probably taking marching orders from Nunnally.
Euphemia on the other hand I could see Exalting as a Solar, probably as a Zenith or Eclipse caste. She's highly motivated to do the right thing, and she actually managed to convince canon Lelouch to go along with her kinder, gentler plan rather than continuing his violent rebellion. If that isn't worthy of a Solar Exaltation I don't know what it.
It's meta-gaming though, IC we have no idea where's Euphemia at the moment (unless more spying).
However if we can contact Suzaku and put him somewhere not-Japan then we can safely ensure the meeting would not happen, for now of course. Encouraging him to do "My life is nothing and I will work to death." is something I doubt Lelouch would come up with.
I definitely agree here. Lelouch has no IC reason to even suspect the two would meet, and depending on our actions with Clovis they might not unless Euphemia comes to Japan for some reason. Also, Lelouch wouldn't want Suzaku to be suicidal because Suzaku is a real friend to him, regardless of their differences in opinion, so at the very least he wouldn't encourage it.