Lugia has a four-star Speed stat in the Pokeathlon, so he would do fine in the Speed Pokeathlon, especially since he has decent stats all around.
However, Lugia's Speed stat can't be improved with Pokejuice since four stars is its maximum potential. If you are willing to use Pokejuice to find the best possible Pokemon for the Speed Pokeathlon, there are much better alternatives presented on this list here that might prove to be more effective.
Hope I helped. :)