I read a bit about the Spanish Maquis on wikipedia, but I find somehow hard to comprehend how strong those Anti-Franco-troops were, how they became guerilla forces or fled to France.
Was the Franco regime and its control over the population and the approach against Republican ideas after the civil war comparable to the actions of the Nazi-regime against democratic and communist people in Germany?
Most of the Republican leadership went into exile. Those who didn't were largely imprisoned or killed.
I will highlight one such Republican leader--José Antonio Aguirre. This man was president of the Basque region during the Spanish Civil War. After the Basque region fell, he went into exile. He first went to France, but was in Belgium when Germany invaded the west. He tried to flee to a port to escape. That port's name? Dunkirk. It didn't work out. He was stuck in France with the Gestapo looking for him. In a show of great personal courage, he went to Berlin under a false identity. After gaining some assistance, he made his way to neutral Sweden. From there, he fled to Brazil, and then to Uruguay. After WWII he came to the United States and was a lecturer at Columbia University. Later, he would return to France, where he died in 1960. He only returned to his homeland to be buried.
The Nationalist regime (and later Franco's government) brutally repressed the Republicans during and after the war. During the conflict, over 100,000 noncombatants were killed by the Nationalists (compared to estimates of 35k or so by Paul Preston, or as many as 70k by others). Republican politicians, union leaders or members, journalists, political theorists and agitators, and teachers and other intellectuals were specifically targeted. Many were simply murdered. Others were imprisoned, tortured, humiliated, or raped. Disarmed prisoners were butchered. This brutality was widespread, ongoing, and largely unchecked by Nationalist leaders. The atrocities committed during the war did not stop with the cessation of hostilities. Opponents continued to be killed, imprisoned, violated, repressed, and more--sometimes with a trial and sometimes without. In an effort to please the west after WWII, some of these activities were reduced in order to make alliances with the US more acceptable.
I'm not an expert on Nazi practices outside a very narrow scope, but Franco's regime was certainly very harsh on dissidents, especially during the civil war and in its immediate aftermath.