I work in Healthcare Messaging in Canada; specifically, I work in messaging in British Columbia, where we work primarily with Point of Service applications and Clinical Information Systems that generate and consume messages in the HL7 v2 pipe and caret notation, with a foundation of registries and repositories that use a version of HL7 v3 Messaging XML. More or less, this follows Canada Health Infoway's iEHR blueprint; however, following Infoway's original blueprint, we would have HL7 v3 at the Point of Service as well as the foundation.
HL7 v2 is still used extensively in other Canadian jurisdictions. Some use v2 almost exclusively. In Canada, we have a mix of v2, v3, with some CDA. The United States, on the other hand, never embraced v3, creating a desperate need for a better messaging layer. In this case, FHIR will accomplish things in the U.S. that v3 could not, and that leaves Canada in a challenging position - continuing on with further investment in HL7 v3 makes little sense. Like CDA before it, FHIR can be used to augment these projects; there are enough similarities between FHIR XML and v3 Messaging to make this plausible.
Ongoing CDA projects in Canada are bound to continue as such, which will be worth paying attention to as CDA projects in the States start shifting to HL7 FHIR as an implementation standard. The message from Infoway recently here is to use the appropriate standard for the work at hand, and I expect this message to percolate on both sides of the border; but what does this really imply? How do you decide? For new business cases which would previously have required a document standard like CDA, HL7 FHIR is going to be compelling, as well as low risk, local, and greenfield projects.
Worth noting is the four ways that FHIR can be used. As previously discussed, FHIR supports both Messaging and Document use cases; but, perhaps more importantly, FHIR also supports both REST and Service use cases. In addition, FHIR is in many ways custom built for the security and transport requirements of mobile use cases, and contains resource definitions that will enable social use cases like circle of care and information provenance. For existing health information systems and applications, as well as new, FHIR creates new ways to expose, access, and share information; providing not only tools, but also challenges.