Geoexchange systems with water to water heat pumps as well as traditional water to air heat pumps have been used for over 30 years in Canada. It's all about sizing the loops properly with very good soil conductivity testing and information. Typically the cold climate approach is to size the loops and geoexchange system for a balanced heating and cooling load profile, and if skewed to more heating that cooling, use more geoexchange tube, and use a supplemental boiler for the peak heating load conditions.
Yes, there are some examples where some well meaning folks have created permafrost, and have lost the use of the system until the ground temperatures recovered (years sometimes), usually as a result of undersized geo fields and poor soil conductivity assumptions.
There are other examples where solar water heating panels are used to "charge" the ground temperature for winter heating - keeps the geo field small, but with the additional expense of the solar panels (more tube or solar panels? Do the math for the project)
Another example of geoexchange for a heating dominated climate is the housing project on Okotoks, Alberta, where all the homes are equipped with solar water heating panels which dump excess heat into a set of closely spaced vertical tube loops to heat up a big chunk of earth, then use that heat all winter without having to rely on an actual water to water heat pump. Drake Landing - weblink:
