About US: everybody heard "no taxation with no representation", and this is a simpler summary of the original colonial pact (Edmund Burke wrote a lot about this):
US colonies would not pay tax to England (only small local taxes to limited local governments)
US colonies would import/export only from/to England (monopoly)
US colonies could not build various kinds of
manufactures for more sophisticated goods.
US colonies would not have MPs, and their militias would fight in American Wars, but on the other hand, there would be no large scale involuntary conscription to serve overseas (remember that many RN sailors were conscripted or just judicially sentenced to serve).
This happened because it would be very difficult for the King to tax a distant colony. Even an honest tax collector would be too far from the King and too close to the tax payers. And any dispute would take months to be solved if it depended on transatlantic travels. It was easier to impose the monopoly and tax any commerce in the UK side (and the monopoly means that everything was taxed).
It may be that the taxes imposed by the UK before US independence were not so high, but the amount was not the point: any tax was too much if the monopoly and industrial restrictions were still in place.
Burke (as an English MP) was against the various Acts during the build up to the war, he wanted to keep negotiating, and he was keen to expose the American view point above: the deal was zero taxation on the US side! We must have a colonial pact that does make sense!
And the whole system breaks down if there is large scale smuggling (such as tea). Lots of people loose money on the UK, and taxes are not paid. It also makes sense that when England tried to suppress such smuggling, many american feathers got ruffled, as the smugglers would get rich easily.
If it was decided to have fair representation for all the colonies, to give equal rights to US and UK citizens, then how would all this change? Rights come with responsibilities. Would the Virginia Militia happily be conscripted to fight in Europe or India, just to earn the right to nominate a MP in London - and how would they communicate with their MP in due time?
Another point: colonial pop could be significant, and Parliament districts were setup based on population. Would an Englishman accept that 10, 20, or 30% of his legislators were colonials? And can a parliament really work with factional interests so divergent?
It is unfair to say 'it is unfair', if you do not have an alternative workable arrangement.
Colonial history is full of strange arrangements due to the difficult of managing and taxing these transcontinental Empires. For example the various Companies: the Dutch VOC, the English EIC, and even in the XIX c, the Russian-American Company - the state is just passing the buck to private or semi-private enterprises. And Portugal completely gave up collecting custom taxes on Rio de Janeiro: The Sá family got the hereditary right to collect custom taxes for themselves in return of securing and developing the colony. But when the Dutch invaded Angola, they raised a private army to expel the Dutch from Luanda, as they depended on Angola to buy slaves and sell cassava flour.
Another Brazilian-Portuguese example: when Brazil was elevated from colony to kingdom in the XIX c., Brazil got MPs in Lisbon. But, although the free population of Brazil and Portugal were almost the same (3 million), Brazil only had a handful of MPs, and the Brazilians obviously resented it. But how would the Portuguese accept a fair equal-rights distribution? Even if so, how would the parliament work if 50% of MPs were Brazilians?