If the police arrest you without having reasonable grounds to do so, they have likely violated your right not to be detained unreasonably under section 9 of the Charter, which could result in a favourable outcome for you – such as evidence needed to convict you being excluded (not “let in”), or the charges against you being withdrawn – which basically means dropped. The police know this, so they are usually careful about gathering as much evidence as they can before they charge you. This can take a long time. Sometimes police spend years investigating someone before they charge them.