From a legal point of view Scotland was an independent nation identified as Scots most likely from the kingship of Giric in 878 until the Act of Union in 1707.
But from 1290-1357 there were dynastic conflicts in Scotland that resulted in English possession of some Scots territory and the existence of Scotland as an English client state.
That ended in 1357, making Scotland independent in both law and fact.
To accept the Union is voluntary one must obviously ignore the genocidal realities of little matters like the massacre that was Culloden and the Highland Clearances:
The Act of Union took place in 1707.
The Battle of Culloden took place in 1746.
The Highland Clearances began in 1725 or 1762 depending on your definition.
All this took place well after the Act of Union, not before it.
It is obvious that the Highlanders opposed Union. It is also obvious that they comprised less than 25% of the population.
The Union was voted on in the Scots Parliament and the Lowlanders, being three times as numerous as the Highlanders, carried the vote.
Wideawake:
1--The English did not 'conquer' Scotland in 1290,in fact that year the two nations signed the Treaty of Birham which specifically states that England had no legal right to claim overlordship of Scotland.
2--The physical occupation of Scotland took place only in 1296,not 1290.
3--Not only did the Scots expel the English in 1314 from Scotland after Bannockburn,BUT you are amazingly ignoring the 1328 Treaty of Northampton where England legally recognised Scotland's existance as an independent nation.