The Canon has a larger sensor. It will produce images that are less noisy and have higher Dynamic Range. However, the sensor technology is not identical, and the gap in performance is not as big as the difference in sensor size would suggest. Instead of the 7/6 stop difference in sensor size, you get a 5/6 to 1/3 stop difference in performance, depending on ISO level.
The Canon has a higher pixel count which will help with sharpness and cropping.
So the 5DIV has higher IQ potential than the X-T2, but perhaps not so much higher as to justify the difference in system price.
You might also want to consider what lenses you would need on each body, and consider their shooting envelopes, performance, and cost. A pro wedding photographer shooting Canon EF is probably using 16-35, 24-70 and 70-200 f/2.8 lenses. Fuji's corresponding lenses are all slower in equivalent terms. Canon's lenses are larger and more expensive.
In the end it is the usual crop MILC vs FF dSLR tradeoff. The Fuji is cheaper, lighter and smaller, but can't match the shooting envelope or potential IQ of the Canon system. The choice comes down to whether the gap in performance is more or less significant to you than the gaps in price and size/weight. That's going to vary between different people. There is no one right answer.