As Phil says what 'pro' work will you be doing? I can't honestly think of one area where the Canon M series would realistically be good enough for pro work tbh. Sure the IQ is nice, but the performance wouldn't be up to the job. Perhaps fairly static studio work, but it still wouldn't be my first choice.
Obviously what you choose will depend on budget but I would seriously consider where you see your future and what system you need to invest into for that and one that you are comfortable using. There's no doubt that the market is shifting towards mirrorless and you are entering a time when mirrorless cameras truly offer top notch performance, with cameras like the Sony A7-iii, A7R-iii, A9, Olympus EM1-II, and Fuji X-T2. Nikon will also be announcing it's first FF mirrorless in the next few days, although what the cost will be, when it will be released and how good it will be is anyone's guess at the mo.