In case someone else comes across this…
I created the parameters as a List and then in the SqlQuery call I passed it with a .ToArray(). Worked for me. Here’s the modified code below…
var parameters = new List<object>();
parameters.Add(new SqlParameter("param1", param1Value));
parameters.Add(new SqlParameter("param2", param2Value));
IList<XXXViewModel> XXXList =
_context.Database.SqlQuery<XXXViewModel>("spXXX @param1, @param2", parameters.ToArray()).ToList();