A 55-year-old man presents with polyarticular joint pain and morning stiffness lasting 2 hours for 4 months. Examination shows synovitis of the metacarpophalangeal and proximal interphalangeal joints bilaterally. Rheumatoid factor and anti-CCP antibodies are positive, and inflammatory markers are elevated. According to Canadian rheumatology guidelines, what is the most appropriate initial disease-modifying treatment?