Could Tecumseh’s plan for a Pan-Indian Confederation, a nation of unified Indians stretching from Canada to the Gulf of Mexico, have worked, if his brother, Tenskwatawa, had not prematurely engaged the United States forces at Tippecanoe?
The Pan-Indian Confederation would not have succeeded. Although it would (and probably was) useful in negotiating with the United States, militarily it would (and did) fail. Simply put, the Native Americans were outmanned and outgunned. Even if they could have put aside all tribal differences and acted as a cohesive force, they did not possess the type and quantity of armaments to deter the US. Also, there were simply not enough Natives to counter the swelling tide of Americans and Europeans invading and spreading over North America.
Of course, this is simply a matter of speculation, but here goes.
I am inclined to strongly doubt that this could have worked. I believe this to be true because there is no very good example of Indian nations joining together to effectively fight against white settlers. Indian nations tended to each go with what they thought was good for their particular tribe. The tribes did not always agree on what was good, not least because many of them had were enemies.
Nowadays, we see all the Indians as monolithic -- they were "The Indians." But in truth, they did not see themselves as a monolith -- they saw themselves as individual tribes and this sense would have made it hard for them to remain effectively united. (Just as all the white people of Europe find it hard to unite in a European Union...)