I am an Indian citizen and I was charged with criminal harassment in Canada. I am looking to marry a girl who is a German citizen. Can I enter Germany after marriage and get German citizenship?
NO, and yes.
Germany is a member of the Schengen Area, whose law is relatively lax. Questions about criminal convictions are not asked when applying for a Schengen visitor/business visas, and border agent and landing cards (there aren't any) don't ask this either.
If any officials or forms ask you if you have a criminal history, you still have to answer truthfully, but in general if its not more than 3 years of imprisonment, or crimes involving alien smuggling or drug offences that resulted in more than 2 years of imprisonment, then generally they will not refuse you entry or visa on that ground.
Germany has specific rules that state anyone convicted of an offence relating to public order with a sentence of more than 3 years, a drug offence with a sentence of more than 2 years, and any offence related to alien smuggling is deportable (a "must deport"). Like the UK they are more concerned with offences committed in their country, rather than outside of the EU.
If you lie on any visa application or question by officials, that is a "can deport".
So, in other words, you can ENTER on a vistor visa.
However, if you want to marry a German girl, and stay in Germany, you'll need a residence permit. And a residence permit, you won't get with a recent (or serious) criminal history. So while you can enter, entering makes no sense.
Also, it could be difficult finding work with a criminal record.