Brown the andouille in the oil in a skillet over medium-high heat, 4 to 5 minutes, then transfer it to a 6-quart slow cooker.
Cook the onion and bell pepper in the skillet for 4 minutes and add the garlic for 30 seconds.
Transfer the vegetables to the cooker and stir in the tomatoes, broth, Cajun seasoning and salt.
Cover and cook on low for 4 to 4 1/2 hours.
Stir in the cream, switch to high and add the shrimp in one layer.
Cover and cook until the shrimp are opaque and curled and reach 145°F, 15 to 25 minutes.
Boil the linguine until al dente, drain it and toss it with the Cajun sauce, shrimp and sausage.
Finish with the scallions and serve immediately.