I'll follow up for Dr. Peter for you. My initial response was to tell you that there appears to be more than one thing going on in James as is common in dogs of his age. Now that i see that he suffered from a rectal cancer, by the principle of Occam's Razor, it's most reasonable to assume that the blood in his stool (hematochezia) is due to a recrudescence (relapse without cure in between events) of the cancer. Blood in the urine (hematuria) may also indicate cancer - often a transitional cell carcinoma of the bladder and/or urethra but rectal cancer can metastasize to the urinary tract and other distant sites. Urinary calculi (stones) and a bacterial urinary tract infection (UTI) should be considered as well.
Excessive panting can represent both medical and behavioral problems. It's often seen with elevated ambient temperature, exercise, anxiety, or perceived pain. To confound the diagnosis further, it's also seen with fever, narcotic administration, glucocorticosteroid (prednisone, e.g.) therapy, Cushing's disease, hyperthyroidism, hypocalcemia, pheocromocytoma (an adrenal gland tumor), cardiac disease, tachyarrhythmias (fast irregular heart rates), brain disease and obesity.
I would approach James by performing a thorough physical exam including digital palpation of his rectum. A senior/geriatric diagnostic panel of blood and urine tests should be included in his exam and X-rays of his chest and ultrasound of his abdomen are indicated looking for post-operative metastatic lesions. Please respond with further questions or concerns if you wish.