It sounds like you're referring to Franklin's Plan of Union and later Articles of Confederation (not the Articles of Confederation, different ones). There were other proposals to integrate Native Americans and the newly arrived Europeans, but they sought to unite under the crown. Franklin was the first to say at the highest level that we should integrate into an independent nation from the crown and ally with Native nations. 21 Jul 1775 he proposed this plan of an independent America, nearly a full year before we would declare independence (and a few years before the Articles of Confederation that were adopted by the states would be written). It said;

ART. X. No Colony shall engage in an offensive War with any Nation of Indians without the Consent of the Congress, or great Council above mentioned, who are first to consider the Justice and Necessity of such War.

ART. XI. A perpetual Alliance offensive and defensive, is to be enter'd into as soon as may he with the Six Nations; their Limits to be ascertain'd and secur'd to them; their Land not to be encroach'd on, nor any private or Colony Purchases made of them hereafter to be held good; nor any Contract for Lands to be made but between the Great Council of the Indians at Onondaga and the General Congress. The Boundaries and Lands of all the other Indians shall also be ascertain'd and secur'd to them in the same manner; and Persons appointed to reside among them in proper Districts, who shall take care to prevent Injustice in the Trade with them, and be enabled at our general Expence by occasional small Supplies, to relieve their personal Wants and Distresses. And all Purchases from them shall be by the General Congress for the General Advantage and Benefit of the United Colonies.

He also invited other colonies to join;

Any other and every Colony from Great Britain upon the Continent of North America and not at present engag'd in our Association shall may upon Application and joining the said Association be receiv'd into this Confederation, viz. [Ireland] the West India Islands, Quebec, St. Johns, Nova Scotia, Bermudas, and the East and West Floridas; and shall thereupon be entitled to all the Advantages of our Union, mutual Assistance and Commerce.

Dr Franklin had been influenced by his connection to some of the earlier conventions and most particularly by a speech from an Onondagan Chief urging the colonies to follow the lead of the Six Nations to preserve themselves indefinitely. Franklin immediately published the speech from his printing house and spread the idea, this happening in the 1750s.

Any of that ring the bell? Happy to answer follow-up questions you may have about the Articles, Dr Franklin, the Six Nations, or pretty much anything else related.

Not quite sure what your teacher was talking about. The tricky part is that phrase "mix together". There may have been a historical figure with actual egalitarian intentions. Ben Franklin often had good things to say about the Native Nations, but I don't know if he recommended "mixing together" of the Native Nations and the US . If by "mix together" you mean Native Americans assimilating into the US , then Thomas Jefferson is likely the Founding Father. As President he of course had swung the deal with Napoleon to get the Louisiana Territory, and that came with a big Native American population. He wrote to his appointed governor of the Ohio Territory, William Henry Harrison, a famous long letter on February 27, 1803 laying out his ideas. One important section:

our settlements will gradually circumbscribe & approach the Indians, & they will in time either incorporate with us as citizens of the US. or remove beyond the Missisipi. the former is certainly the termination of their history most happy for themselves. but in the whole course of this, it is essential to cultivate their love. as to their fear, we presume that our strength & their weakness is now so visible that they must see we have only to shut our hand to crush them, & that all our liberalities to them proceed from motives of pure humanity only. should any tribe be fool-hardy enough to take up the hatchet at any time, the seizing the whole country of that tribe & driving them across the Missisipi, as the only condition of peace, would be an example to others, and a furtherance of our final consolidation.

Notice that it wasn't as though a deep bond of trust and understanding would be fostered between the Native Nations and the US, resulting in an alliance and merger of equals. The Native Americans were primitives, and were to be brought out of their traditional ways and incorporated into the US. And despite talking of " motives of pure humanity" Jefferson would be the first of a number of Presidents who would make kind noises about Native Americans, but would remove them from their territories and give their land to white settlers and land speculators.