Please advise me what I need to do to the canvas if I use unsized and unprimed cotton duck and use acrylic as staining and glazing. Is this OK or do I need to seal the canvas? Are acrylics acidic?
With acrylics, staining can be done directly onto the paper or raw canvas, however if the artwork isn't going to be displayed behind glass, the surface needs to be coated and varnished.

The acrylic paints dry pH neutral. It in itself will not cause natural fibers like canvas and paper to break down like the acids in oils will, however, the artwork should be sealed to protect the canvas from the environment over the years. This is achieved with an isolation coat and then either the Polymer varnish or the MSA Varnish. Done properly, these products can be applied in such a way that they are not noticeable to the viewer.

The recommended brushable isolation coat is 2:1 Soft Gel Gloss/water. Applied in thin coats, you should still be able to see the weave of the canvas. Once a gloss remains over the entire surface, the varnish is then applied. It is good to experiment with the exact sheen that mimics the raw canvas. It may be our satin or matte formula neat, or it may be a blend of the products to achieve the desired look.

If you intend to use acrylics under oil paints, apply the stains directly to the canvas, then apply several coats of the isolation mixture, then a coat or two of Matte Medium. This should allow adhesion of the two paints and protects the canvas from the oil. To check for this, make a test panel, apply the acrylics as mentioned, then apply a few drops of linseed oil onto the canvas and watch it over the next few weeks. If the drop remains on the surface, then you have adequate protection from oil penetration.