Personally, I would do a complete pond renovation and start over. The agony and headaches involved in trying to fix the problem will be worse than the patience required to start all over and wait for your newly stocked fish to grow. Plus, I believe it'll be cheaper to poison and restock rather than try to renovate the current fish population... This is predicated on the knowledge that however those unwanted species(GSF, BC) got in there, will not get back into the pond after renovation.
If you do not go the fish poison route, I would highly recommend you invest in a couple of fyke/hoops nets. These are the least utilized method of fish management but IMO the most efficient and effective in removing the exact fish you want and only those fish... They capture everything. However, you can release the species and sizes you want released and those you want removed can be taken out... There are several companies that sell them, if interested I can provide a list.
Relying on high end predatory species like large Esox(pike and musky) carries risks. They often don't want to cooperate by eating what they want to eat, not necessarily the species and size of fish you want them to eat. However, you have a large enough pond that they are certainly an option with proper management if you don't want to go the fyke/hoop net route.
