Many thanks to L for the info!
The Alliance of Canadian Cinema, Television, Television and Radio Artists (ACTRA) is the union of more than 23,000 professional performers working in English-language recorded media in Canada including TV, film, radio and digital media.
ACTRA has listed Siberia on their ‘Current Productions’ page. They have listed that Carmen Kotyk is in charge of casting. Kari Casting was also listed as the local casting company that will be supplying background performers (extras) for the film. According to their site the Siberia shoot will begin on April 17 and run through May 19, 2017.
Kari Casting has posted on their website that they are working on the Siberia production and have reminded folks to send in their applications for extra roles. From reading elsewhere on their site, they don’t appear to hold open auditions, but contact applications for roles they may be appropriate for. According to their site, the Siberia shoot is scheduled for April 3 through May 15, 2017.
Note: Of the three start dates that have been reported for Siberia, I’d say that April 17 is the more likely start date.